Determination of Shear Viscosity of Molecular Nitrogen (N₂): Molecular Dynamic Hard Rotor Methodology and the Results

Abstract

Determination of shear viscosity of molecular nitrogen (N(2)) by molecular dynamics (MD) in the high density range needs explicit incorporation of the rotational motion and therefore precise knowledge of angular dependence of N(2)-N(2) intermolecular potential. Newly designed Couette flow nonequilibrium molecular dynamic (NEMD) simulation procedure employs corrugated moving boundary, coupling the moving walls to translational and rotational motion exactly. Low density data on nitrogen viscosity show good agreement between MD data and experiment, confirming the radial dependence of the potential derived from quantum mechanical (QM) high precision calculations (coupled-cluster singles-and-doubles with a perturbative triples corrections [CCSD(T)]). Additionally, the angular dependence of the potential is verified using shear viscosity data for high density region, obtained from newly developed molecular dynamics (MD) simulations. It was demonstrated that the corrugated wall flow simulations provide results that are independent of the details of wall potential, fulfilling a basic requirement for application of MD simulations. These results are in good agreement with the equilibrium molecular dynamics (EMD) viscosity, derived from the Green-Kubo formula. Derived analytical dependence of the shear viscosity on the density and temperature shows that the MD data are in good agreement with experiment. Thus, MD simulations indicate that the CCSD(T) potential angular form is sufficiently precise for determination of the viscosity in a wide range of temperature and pressure.

Viscosity of Fluid Nitrogen to Pressures of 10 GPa

“…Strak and Krukowski used molecular dynamic simulation, coupled with the appropriate Green–Kubo relation, to predict viscosities of nitrogen at 700 and 1500 K, up to a maximum density of 1.8 g/cm 3 ; these predictions are included in Figure . The short extension from current, 673 K data indicates that simulations of the 700 K fluid underestimate viscosity by about a factor of 2 at the higher densities.…”

“…Figure1. Measured viscosities are plotted on isotherms against pressure, along with results from molecular dynamic simulations (SK) 6. Solid lines are from eq 1, extended by short dashes in the metastable region above the melting points; long dashes show a 1500 K isotherm as predicted by eq 3…”

A study of Ar-N2 supercritical mixtures using neutron scattering, molecular dynamics simulations and quantum mechanical scattering calculations

“…Potoff et al [40] presented a non-polarizable all-atom transferable potential for phase equilibria (TraPPE) force field for N 2 which could reproduce the VLE experimental results. Recently, Strak et al [41][42][43] used ab initio quantum mechanical calculations to obtain the intermolecular PES, and to perform MD calculations of the equation of state and shear viscosity. More recently, Cioce et al [44] derived two five-site potential energy function for N 2 , one including and one neglecting explicit induction effects, and used two differing sets of mixing rules.…”